Oxyacetylene torches designed for powder spraying are sometimes subject to back flash if the torch tip encounters an obstruction, or is accidentally advanced too close to the workpiece or is subjected to a sudden change in ambient pressure conditions in the vicinity of the torch outlet. Such back flashes can be quite hazardous to the workman and can result in an explosion in the powder reservoir or in the loss of powder to the atmosphere.
Various proposals have been made to arrest such back flashes or to minimise the potentials for injury to the equipment or to personnel. Usually such expedients provide means for shunting the back flash pressures to the atmosphere in some manner bypassing the powder contents of the reservoir. Examples of such expedients are disclosed in U.S. Pat. Nos. to Fleischhacker et al 3,476,320; and Hawk 3,415,449. These and the like expedients have proven quite satisfactory in use but some users find it a simple matter to circumvent or deactivate the safety device by applying a cover or other sealant means over the outlet end of the back flash preventer. Usually this outlet is associated with the power feed tube and is in communication with the atmosphere through the sidewall of the powder container or hopper and is so constructed as to avoid loss of powder while quickly and freely venting back flash pressure to the atmosphere independently of the main powder supply. Such a cover renders the back flash preventer inoperative and poses dangerous conditions for both the equipment and the operator.